Boreholes are created by drilling into the earth using a rig. The rig drives a bottomhole assembly (BHA) on a drill string to create a hole. The BHA comprises a drill bit, which is provided with sufficient weight-on-bit (WOB) to break the rock. The BHA also may provide directional control of the drill bit and may use sensors to take down hole measurements of actual drilling conditions.
Fluid, or “mud,” is pumped down hole through a drill pipe while drilling. The mud cools the drill bit, circulates through the borehole, and returns drill cuttings, such as sand and shale, to the surface. The cuttings are passed through a shaker which strains the cuttings from the mud, and through a centrifuge which separates the sand from the mud. The cleaned mud is then returned down hole through the drill pipe.